This project will attempt to demonstrate the practical utility of wavelength-modulated fluorescence. The theory of the technique was developed, and benefits in selectivity demonstrated for model systems, nearly ten years ago. We believe the technique has a tremendous potential to improve the selectivity of fluorometry in clinical analysis. A stringent test of the realizable benefits of wavelenght-modulated fluorescence will be made by using such a system to determine compounds of clinical (drugs, vitamins) and neurochemical (catecholamine and indoleamine neurotransmitters and metabolites) interest in plasma and urine samples. Initial work will involve the construction of a wavelength-modulated fluorometer suitable for both flowthrough and static cell measurements. Our prior experience in modifying the instrument prototype and the cooperation of the designer of the original instrument insure the success of this phase. The sensitivity of the instrument will be optimized, and detection limits established, for the compounds of interest. Parameters affecting signal-to-noise ratios will be well characterized, these include: wavelength modulation interval, modulation frequency, filter bandpasses, and phase angle-shift. The selectivity of the fully characterized instrument will be tested by the method of standard addition using pooled human urine and plasma samples. In some cases the enhanced selectivity expected to result from the use of wavelength modulated fluorescense might enable the determination of drugs, vitamins, and neurochemicals in unpurified physiological samples. However, the combination of wavelength modulation with high performance liquid chromatography (HPLC) seems to offer the greatest potential. The coupling of two highly selective methods should allow a number of important compounds to be determined with greater ease and accuracy. Direct comparison of the technique to the popular method of HPLC-fluorometry will be made by inline detection of HPLC column effluents using both methods. A range of unpurified and partially purified urine and plasma samples will be separated and analyzed. The optimization of the new simplified methods which we expect to develop will follow this broad survey.